1. Field of the Invention
The present invention relates to an apparatus and a method for controlling an automatic transmission for a vehicle; and, more particularly, to a technique for controlling a shifting output timing of the automatic transmission in such a manner that, in a up-shift under a high-load condition, e.g., towing, driving up a hill, or the like, the engine rotational speed during an inertia phase start point approaches an engine rotational speed in a predetermined range of a target maximum engine rotational speed as quickly as possible.
2. Description of the Related Art
For a vehicle, in which the power-on and up-shift operation of an automatic transmission is executed in response to a shift command, there has been known a shift control apparatus for automatic transmissions, which controls the shift point of an automatic transmission such that the engine rotational speed at an inertia phase start point in an up-shift mode with a fully depressed accelerator pedal or a fully open throttle valve approaches a preset engine rotational speed zone. For example, such a conventional shift control apparatus is described in Japanese Patent Application Publication No. JP-A-2003-28284. The shift control apparatus uses a shift line (shift pattern) in which, when an automatic transmission performs or executes an up-shift operation when the accelerator pedal is fully depressed or a throttle valve is fully open (100%), the shift control apparatus controls the automatic transmission such that the engine rotational speed approaches a high rotational speed, without entering a preset red zone or a fuel cut zone beyond the red zone. Further, the shift pattern of the shift control apparatus varies according to the carrying capacity of a vehicle, thus enabling the automatic transmission to execute the shift operation at an optimal point.
When a vehicle having a conventional shift control apparatus drives in a state in which resistance to driving varies greatly such as when driving up and down hills or towing, the rising ratio or the rising speed of the engine rotational speed after a shift operation (shift output) varies. Thus, the shift control apparatus cannot provide a full throttle up-shift operation, wherein the engine rotational speed can approach a high rotational speed, without entering a preset red zone or a fuel cut zone beyond the red zone. In an effort to solve the problem, Japanese Patent Application Publication No. JP-A-2004-316845 describes a technique in which a plurality of learning sections is provided according to the state of driving of a vehicle, and the shift point is learned and corrected in every learning section, so that the learning of the shift point can be executed during driving conditions such as those encountered when driving up a hill or towing, which affect vehicle acceleration.
However, when a small number of learning sections is provided, the shift operations may be indiscriminately executed at some shift points within the learning sections despite a wide range of vehicle acceleration, so that shift precision may be reduced. Meanwhile, when a great number of learning sections is provided, the learning of the shift points in the sections may take excessive time and may increase the capacity of the memory of the shift control apparatus, thus increasing the cost of the shift control apparatus.